In order to convert fluoroelastomer raw materials and compounded gumstocks thereof into finished elastomer goods or articles with desired properties, it is common to incorporate into or mix with such fluoroelastomer gums various chemicals and compounding ingredients, each having a specific function both in the processing and vulcanization of such fluoroelastomer base materials and in the end use thereof.
One type of such ingredients is process aids, which are commonly used to modify the viscosity and toughness of the raw or unvulcanized fluoroelastomer, and/or to aid it in a specific manner, e.g. during or in the processing thereof, e.g., mixing, milling, mastication, shaping, or vulcanization of the gum or gumstock. In particular, process aids are used for assisting flow and are generally essential for easy mould release, to minimize mould fouling and to achieve a smooth surface finish notably on profiles and sheets.
Various materials have heretofore been prepared and used as process aids, such as various waxes and oils. For example, in the processing of fluoroelastomers, e.g., copolymers of vinylidene fluoride and hexafluoropropylene, which are particularly difficult to process, mixtures of oleic acid and low molecular weight polyethylene have been proposed (see U.S. Pat. No. 4,328,140 (RAYBESTOS MANHATTAN INC) 4 May 1982) as have fatty acid esters (e.g. carnauba wax and montan wax) (see U.S. Pat. No. 3,753,937 (MINNESOTA MINING & MFG)) and diorgano sulfur oxide compounds (see U.S. Pat. No. 4,287,320 (MINNESOTA MINING & MFG) 1 Sep. 1981).
Also, fluorinated oils have been suggested as process aids in fluoroelastomers composition, as taught in U.S. Pat. No. 4,278,776 (MONTEDISON S.P.A.) 14 Jul. 1981 and in EP 0099079 A (MONTEDISON S.P.A.) 25 Jan. 1984.
Although conventional process aids provide many useful benefits in the processing of fluoroelastomers, as mentioned above, the processing of these materials has presented a multitude of problems, due to the chemical nature of the fluoroelastomers and its poor compatibility with ordinary process aids and their often severe use requirements.
Oxygen-containing additives (e.g. esters), while generally compatible with the fluoroelastomer, are extractable, for example, by lubricating oils and hydraulic fluids. Resulting cured articles are thus subject to shrinkage and deformation during cure and use.
When poorly compatible additives are used (e.g. polyethylene or fluorinated oils), exudation at the flow front may cause knitting problems due to the extreme surface lubricity and undue bleeding during moulding and curing. Also, certain process aids may affect cure rate and scorch safety. In a nutshell, traditional process aids do not perform as well as desired, some of these interfere with the curing of the gum, and others adversely affect the final physical and mechanical properties, shape, and visual appearance of the cured fluoroelastomer or finished goods.
Process aids for fluoroelastomer compositions, easy to incorporate, enabling outstanding mould release with virtually no mould fouling in injection/extrusion moulding, and/or enabling easy extrusion with outstanding surface aspect with substantially no die bleed, while having no adverse affect on the curing of the fluoroelastomer or on other desired properties of the fluoroelastomer compositions or finished goods therefrom are thus still considered a current shortfall in the art.